This invention relates generally to catadioptric imagers, and, more particularly, to an optically fast, telecentric catadioptric imager design.
A catadioptric imager is a device comprised of a combination of both refractive and reflective surfaces that is commonly used to image light emitted or reflected by a given object or scene onto a focal plane where it can be readily observed or recorded.
As an example of an application that underscores the need for improved catadioptric imager designs, a hyperspectral imager is considered below.
A hyperspectral imager, or imaging spectrometer, is a device that is commonly used to examine the spectral, or wavelength dependent, content of an object or scene. These devices are typically comprised of an imaging fore-optic system that images light emitted or reflected by a given object or scene onto a slit element that transmits a single line portion from the image of the object or scene. This slit typically serves as the object of a spectrometer optical system that in turn re-images the light transmitted by the slit to another location while dispersing this light according to its wavelength in a direction orthogonal to the orientation of the slit element. In this manner, each slice of the object or scene is decomposed into a two-dimensional data array, and by scanning the object or scene in line-by-line increments, a three-dimensional data cube is formed.
In order to maximize the throughput of optical energy from the imager fore-optics to the spectrometer optical system, it is desirable that the imager be substantially telecentric in image space. A telecentric optical system is one that has its exit pupil located at infinity, and corresponds to the condition where the optical chief ray is parallel to the optical axis in image space (see, for example, Milton Laikin, “Lens Design,” ISBN 0-8247-0507-6, p.265).
Recent developments in compact infrared spectrometers have created a need for compact infrared imagers to be used as fore-optics. These imagers must be optically fast with little or no obscurations, as well as being substantially telecentric in image space in order to provide sufficient throughput to the spectrometer.
Current infrared imager designs are either too large in size, overly vignetted or obscured, or not substantially telecentric enough to serve as imaging fore-optics for use with compact infrared spectrometers in many applications, including but not limited to, unmanned aircraft surveillance and forensic fieldwork.
In the above example, as in most optical systems, alignment of the optical components presents assembly and design challenges. Many of the current catadioptric imager designs present alignment challenges.
There is therefore a need for an optically fast catadioptric imager design that is more compact in physical size than current fast catadioptric imagers.
Furthermore, there is also a need for a compact catadioptric imager design that is optically faster than current compact catadioptric imagers.
Furthermore, there is also a need for an optically fast compact catadioptric imager design that has a smaller degree of obscuration than current compact catadioptric imagers.
Furthermore, there is a need for an optically fast compact catadioptric imager design that is unvignetted.
Furthermore, there is also a need for an optically fast compact catadioptric imager design that is telecentric in image space.
Furthermore, there is also a need for a catadioptric imager design that is easier to align than current catadioptric imagers.
Still further, there is also a need for a catadioptric imager design that provides a combination of the characteristics described above with superior trade-offs than have been previously attainable.